Various data streams for compressing and encoding a video signal and an audio signal at low bit rates have been standardized recently. Among other things, system streams compliant with the DV standard (or Consumer Digital VCR SD standard) and MPEG-2 System standard (ISO/IEC 13818-1) are well known as such data streams. System streams include the three types of streams—program streams (PS), transport streams (TS) and PES streams. Each of these data streams may be stored on an optical disk, for example, so as to comply with a predetermined standard.
Recently, data recording apparatuses (such as consumer camcorders) for realizing a “post-recording” operation with such a data stream have just become popular. As used herein, the “post-recording” operation refers to an operation of newly recording different audio once video and audio have been recorded. By performing such a post-recording operation, the newly recorded audio can be reproduced synchronously with the video instead of the originally recorded audio.
In the following description, the originally recorded audio will be referred to herein as “original audio”, while the newly recorded audio “substitute audio”. Also, video with the original audio will be referred to herein as a “moving picture”. Furthermore, data representing the video will be referred to herein as “video data”, data representing the original audio “original audio data” and data representing the substitute audio “substitute audio data”.
The post-recording is usually realized by performing the following two steps. In the first step, a moving picture is recorded in a recording mode that enables the post-recording. In this recording mode, a data stream is recorded so as to have a data structure that enables future recording of substitute audio. Next, in the second step, the substitute audio is recorded while the moving picture recorded is being played back. If the post-recording is carried out in this procedure, an apparatus for playback (data playback apparatus) can play back the video and the substitute audio synchronously with each other. The user specifies the video and audio data to play back synchronously with each other and the playback timing thereof by describing a play list. To play back video and other data synchronously with each other in this manner will be referred to herein as “synchronous playback”. It should be noted that the original audio data may be either erased or coexistent with the substitute audio data. In the latter case, the video, original audio and substitute audio may sometimes be played back synchronously with each other.
Also, the second step does not have to be the “real-time” post-recording, in which the audio is recorded while the moving picture is being played back, but may be non-real-time post-recording in which an audio file is copied without monitoring the moving picture.
Hereinafter, a configuration for a data playback apparatus will be described. FIG. 1 shows an arrangement of functional blocks in a conventional data playback apparatus. The data playback apparatus can play back a data stream stored on an optical disk 131 such as a DVD-RAM disk or a Blu-ray disk (BD). In the following description, the data stream is supposed to be an MPEG transport stream (TS). A TS consists of a plurality of packets (TS packets). Each TS packet includes video data and original or substitute audio data.
The data playback apparatus performs the synchronous playback (i.e., playback of video and substitute audio) in the following manner. A reading section 121 gets a TS read from the optical disk 131 by a pickup 130 and subjects it to A/D conversion and other processes, thereby outputting TS packets. A first transport stream disassembling section 165 splits each TS packet into video data and original audio data by way of a buffer memory 172. A video expanding section 111 expands (i.e., decodes) the video data and gets the video data presented on a video display section 110.
On the other hand, while the video data is being processed, the substitute audio data is also processed. First, according to the management information about storage areas on the optical disk 131 as managed by a logical block management section 141, a reading control section 171 for post-recorded data locates the substitute audio data to read. In accordance with the read instruction given by the reading control section 171, the reading section 121 reads that substitute audio data, subjects it to A/D conversion and other processes, and then outputs TS packets including the substitute audio data to the buffer memory 172. In response, the buffer memory 172 stores the substitute audio data in a different area from that of the video data. A second transport stream disassembling section 166 reads the substitute audio data from the buffer memory 172. A D/A converting section 176 decodes the substitute audio data and outputs it through an audio output section 112. It should be noted that a first audio expanding section 113 and the D/A converting section 176 share the common function of decoding the audio data.
After the video data and the original audio data have been recorded, the substitute audio data is recorded separately from those data. Accordingly, in performing the synchronous playback, the pickup 130 needs to move to the storage locations of those data and read them out. FIG. 2 shows the order of operations to be done by the pickup 130 in playing back the video and substitute audio synchronously with each other. In this case, what to read is the video data in a moving picture file and the substitute audio data in an audio file.
First, the pickup 130 moves to the storage location of the audio file on the optical disk 131 to read a certain amount of substitute audio data (Read #0). Thereafter, the pickup 130 seeks the storage location of the moving picture file (Seek #0) and reads the video data (Read #1). Once started to read the video data, the data playback apparatus begins to present the video and output the substitute audio. Then, the pickup 130 moves to the audio file (Seek #1) to read the substitute audio data (Read #2) and then seeks the storage location of the video data (Seek #2) again in this order.
FIG. 3 shows how the code densities (the amounts of data) of the video data and the substitute audio data change with time in the buffer memory 172. In FIG. 3, once read out for decoding purposes, every data is supposed to be deleted from the buffer memory 172 instantly. As shown in FIG. 3, during the seek operations ((2), (4), (6) and (7)), the amounts of the video data and audio data either remain the same ((2)) or both decrease ((4), (6) and (7)). On the other hand, while the video data is being read ((3) and (8)), the amount of the video data increases but that of the substitute audio data decreases. Conversely, while the substitute audio data is being read ((5)), the amount of the audio data increases but that of the video data decreases.
In a single read operation, the pickup 130 reads data from a physically continuous area (which will be referred to herein as a “continuous data area”). The minimum data length of the continuous data area is determined by the recording apparatus during the recording operation. FIG. 2 shows where to define the minimum length D of the continuous data area about the video data. A similar definition applies to the continuous data area of the audio data although its minimum length is not always the same.
To play back the video and the substitute audio seamlessly, the amount of the data that has been read and stored in the buffer memory 172 may not go zero. For that reason, to store a sufficient amount of data in the buffer memory, the minimum length of the continuous data area needs to be defined appropriately when the data should be stored. In that case, seamless synchronous playback is guaranteed as long as recording is always performed at that minimum length. Considering storage efficiency, the minimum length of the continuous data area of the video data is particularly important because a huge amount of data needs to be consumed to do so. This is because the greater the minimum length of the continuous data area, the less easy it is to use the remaining capacity of the given storage medium. For example, according to the techniques disclosed in PCT International Application Publications Nos. WO 02/23896 and WO 03/044796, the minimum length D of the continuous data area for the video data is determined with the longest time that it possibly takes to perform each of the seek operations #1, #2 and #3 and the read time to perform the read operation #2 shown in FIG. 2 taken into account. The seek operation #3 is also taken into consideration because if the pickup 130 met across a discontinuity point of the moving picture file (i.e., the boundary of the continuous data area), then the pickup 130 would have to move unintentionally, thus taking an extra time. It should be noted that the seek operation #3 shown in FIG. 2 corresponds to inner-V seek (7) shown in FIG. 3. However, as FIG. 3 shows a worst case, the period of time corresponding to the read time of the moving picture file between the seek operations #2 and #3 shown in FIG. 2 is supposed to be substantially zero.
In this case, the minimum length D of the continuous data area for the video data is derived by the following mathematical equations. Suppose the minimum amount of time it takes to read data from the moving picture continuous data area during the synchronous playback operation is tV-CDA, the data transfer rate during the read operation is Vr, the amount of time it takes to read data from the audio continuous data area during the playback operation for post-recorded data (post-recording playback) is tA-CDA, and the data transfer rate during the playback operation is Vo. Also, the longest seek time to take for the pickup 130 is represented by TSEEK. Furthermore, the data reading unit of the substitute audio file is supposed to be once to twice as large as the data size of the minimum continuous data area (e.g., from 96 kB to 192 kB). In this case, the data size is allowed that once to twice range to make the substitute audio file editable more easily. For example, even if the audio file has been deleted partially, the continuous data area can still be maintained just by processing the editing point and its surrounding portions only.
Then, in FIG. 3, the following Equations (1), (2) and (3) are satisfied:(Vr−Vo)tV-CDA=Vo×(3TSEEK+tA-CDA)  (1)(Ar−Ao)tA-CDA=2Ao×tAo  (2)tAo=tV-CDA+3TSEEK  (3)
Thus, tV-CDA is given by:tA-CDA=(2×Ao×Vr)×3TSEEK)/((Vr−Vo)×(Ar−Ao)−2×Ao×Vo)  (4)
Since Vr=Ar here, Equation (4) can be, simplified into:tA-CDA=3×Ao×TSEEK/(Vr−Vo−Ao−Ao×Vo/Vr)  (5)
Accordingly, if the minimum data sizes of the audio and video continuous data areas are identified by SA-CDA and SV-CDA (bits), respectively, these data sizes are obtained by the following Equations (6) and (7):SA-CDA=Vr×(tA-CDA/2)=3×Ao×Vr×TSEEK/(Vr−Vo−Ao−Vo×Ao/Vr)  (6)SV-CDA=Vr×tV-CDA=3×Vo×Vr×TSEEK×(1+Ao/Vr)/(Vr−Vo−Ao−Vo×Ao/Vr)  (7)
More specifically, if TSEEK=1.2 seconds, Vo=15.57 Mbps, Ao=0.256 Mbps and Vr=20 Mbps are calculated by tv-play=tv-CDA*Vr/Vo and tA-play=(tA-CDA/2)*Vr/Ao, then the minimum value of the video continuous data area will be 18.5 seconds (tV-play), that of the audio continuous data area will be 18.1 seconds (tA-play), the video data size will be 35.7 megabytes (SV-CDA) and the audio data size will be 58 kilobytes (SA-CDA). Accordingly, the size of the audio continuous data area should be 64 kilobytes or more because the size needs to be an integral multiple of an ECC block size.
However, if the minimum length D of the continuous data areas for video data is determined by the technique described above, then the minimum length D could be very long. Considering the defect rate of the disk as well as the condition described above, the minimum length D may correspond to a video playback duration of about 22 to about 23 seconds. For example, if the video data is partially deleted, then empty areas, of which the lengths are less than the minimum length D, will be produced here and there. Meanwhile, to realize a seamless synchronous playback of every moving picture file after the post-recording, every video data needs to be written on continuous data areas, of which the lengths are at least equal to the minimum length D. On the other hand, those empty areas, of which the lengths are less than the minimum length D, cannot be continuous data areas and are not used.
Also, suppose arbitrary playback ranges of a moving picture file are connected together with a play list with audio data played back synchronously. In that case, to guarantee a seamless and synchronous playback of moving pictures and audio, each playback range of the moving picture file needs to be at least as long as the minimum length D and the playback range of the audio data also needs to be at least as long as the minimum length D. In such a situation, if the minimum length of the moving picture data is long, then the play list cannot be a practical one. In other words, to realize a play list that contributes to a practical synchronous playback, the minimum length needs to be short enough. Also, even if the playback range is defined short, the synchronous playback is preferably realized seamlessly and continuously. In addition, not just the recording and playback operations by the originally intended machine but also post-recording and synchronous playback by a machine made by a different manufacturer, of a different type, or of a different price are preferably realized just by following a predetermined format.
The minimum length D may be shortened by introducing a pickup move model as disclosed in WO 003/044796 and as shown in FIG. 62, for example. According to this method, the moving picture continuous data area should be at least as long as its minimum length but less than twice as long as the minimum length.
Based on the following Equations (8) and (9),(Vr−Vo)tV-CDA=2Vo×(2TSEEK+tA-CDA)  (8)(Ar−Ao)tA-CDA=2Ao×(2TSEEK+tV-CDA)  (9)the minimum length can be calculated by:tA-CDA=4TSEEK×Ao(1+Vo/Vr)/(Vr−Vo−Ao−3×Ao×Vo/Vr)  (10)tV-CDA=4TSEEK×Vo(1+Ao/Vr)/(Vr−Vo−Ao−3×Ao×Vo/Vr)  (11)SV-CDA=Vr×tV-CDA/2  (12)SA-CDA=Ar×tA-CDA/2  (13)tv-play=tV-CDA×Vr/Vo  (14)tA-play=tA-CDA×Vr/Ao  (15)If TSEEK=1.2 seconds, Vo=15.57 Mbps, Ao=0.256 Mbps and Vr=20 Mbps, then the minimum value (tV-play) of the video continuous data area will be 13.6 seconds. Even by this method, however, the minimum value should be even shorter.
As described above, there is a growing demand for a method of storing data by using a given optical disk efficiently and a technique of playing back the stored data seamlessly.
A recording method in which a data area for substitute audio data and a data area for moving picture data are arranged adjacent to each other in the spinning direction of the optical disk will be referred to herein as an “interleaving technique”, while a recording method in which those areas are not arranged adjacent to each other will be referred to herein as a “non-interleaving technique”. In FIG. 62, the substitute audio data area and moving picture data area are not arranged adjacent to each other although these areas are associated with each other. On the other hand, FIG. 63 shows an exemplary interleaved data structure for a data stream. If the associated moving picture and substitute audio data are stored adjacent to each other in the spinning direction of the optical disk, then there is no need to perform a seek operation in reading the moving picture data and the substitute audio data. As a result, the minimum data length of the continuous data area can be reduced. In the interleaving technique shown in FIG. 63, a continuous data area for substitute audio data is provided just before an MPEG transport stream, including moving pictures corresponding to a playback duration of 0.4 to 1 second, such that the substitute audio data and moving pictures are played back synchronously with each other. The substitute audio data and the video data are separated from each other at an ECC block boundary and the end of the video data is stored at the end of the continuous data area. According to this method, however, post-recording cannot be carried out in real time on the audio data area. Also, in this method, the audio data areas are dispersed finely. Accordingly, if data is written in non-real time, it will take a very long time to get the write processing done because the write locations are dispersed too much.